Method of recovering oil from oil shale



March 3, 1953 1 W MAR-HN 2,630,307

METHOD OF' RECOVEJRING OIL. FROM OIL. SHALE -Filed Deo. 9. 1948 Pfff-024760 IN VEN TOR.

Patented Mar. 3, 1953 METHOD OF RECOVERING OIL FROM OIL SHALE .lames W. Martin, Tuckahoe, N. Y., assigner to Carbonio Products, Inc., New York, N. Y., a corporation of New York Application December 9, 1948, Serial No. 64,401

7 Claims.

The present invention relates to a v:method of recovering oil from oil shale in situ, and, more particularly, to an improved method of destructively distilling oil shale in situ by using a combustionsupporting gas containing carbon dioxide and oxygen in a critical ratio.

It is well known that heretofore the conventional method of obtaining oil from oil shale inw volved the mining of the shale from the ground, its preparation for thermal, treatment in retorts and its subsequent destructive distillation in re torts heat, the recovery of oils and by-products trom' the vapors and gases distilled from the retorts, and the removal of the residual spent shale yields of volatile hydrocarbons which lessens the cracking of hydrocarbons and which lessens or prevents slugging of the spent shale and thus permits the cinder to remain porous to the flow of oxidizing and other gases.

Another object of the invention is to provide an improved process for the destructive distillation of oil shale in situ in which gaseous products of combustion (flue gases) with highest heat content are effectively utilized.

The invention also contemplates providing an improved process for the destructive distillation of oil shale in situ wherein means will be utilized to limit the formation of viscous tars which will be *from such retorts and its subsequent combustion diicult to remove from the shale beds. under the retorts to supply some of the heat. At- It is a further object of the invention to provide tempt-s have been made to replace the convenan improved process for the destructive distillationai destructive distillation of oil shale in surtion of oil shale in situ wherein means will be used face plants with the usual retort and recovery to limit the formation of hydrogen and light hyequipment with processes which attempted to dedrocarbon gases. structively distill the oil shale in situ in the The invention further contemplates providing ground. These attempts included heating the oil an improved process for the destructive distillashale in the ground by electricity and heating the tion of oil shale in situ wherein a lessening of the oil shale by hot combustion gases piped down into cracking of volatile hydrocarbons will be accomthe shale structure from the surface air burners Dlished. 'burned fuel. Other attempts have involved the It is likewise within the contemplation of the use of air to burn carbonaceous material of the invention to provide an improved process for the oil shale under ground, but this attempt has destructive distillation of oil shale in situ which proven unsatisfactory because nitrogen, which will cause a fixation and recovery of ammonia, constitutes about 80% of the air, tended to dilute 3o urea, and other similar nitrogen compounds. the orf-coming combustion gases and rendered It is also an object of the invention to provide a them unsuitable for proper recovery and commerprocess for the destructive distillation of oil shale cial use. When attempts were made to use pure in situ to eiiect an improved recovery of hydrooxygen, it was found that it was so concentrated carbone. in its oxidizing effect that the temperature of com- Among the further objects of the present invenbustion was uncontrollably high and excessive, tion is the provision of an improved PIOCBSS fOl The problem is to destructively distill the volatile the destructive distillation of oil shale in situ compounds from the oil shale in situ in such a which will prevent relatively high temperatures in manner as to obtain the maximum amount of the the zone of destructive distillation of oil shale, carbon and hydrogen in the oil shale as volatile 4c which will maintain relatively 10W temperatures compounds of these two elements While atin the combustion zone, and which will bathe the iempts have been made to Solve the problem and zone of destructive distillation with carbon dito overcome the shortcomings and disadvantages oxide and thus mix carbon dioxide with resultant of the conventional methods, none, as far as I am hydrocarbons, that Smoking 0f these Volatile hyaware, have been wholly satisfactory in commerdrocarbons is kept at o minimum, that the evolucial operations. tion of hydrocarbons is promoted by the perme- I have discovered 2m improved method of deation action of carbon dioxide, that the formation structively distilling oil shale in situ which overof more volatile hydrocarbons through combinacoines the disadvantages of the prior methods and tion with carbon dioxide is increased and that attempts and which provides the art with new ammonaoal Compounds are nxed with carbon diresults. oxide to prevent their loss in exit gases from conlt is an object of the present invention to prodensers. vide a process for the destructive distillation of Other objects and advantages 0f the invention oil shale in situ by means of low temperature, unwill become apparent from the following descripdol'slound combustion which promotes greater 55 tion taken in conjunction with the accompanying drawing which illustrates diagrammatically an oil shale structure and equipment necessary to carry the novel process into practice.

Broadly stated, the invention contemplates a solution to the vexatious problem confronting the art by effecting a combustion of fixed carbon of oil shale in situ by a gaseous mixture of oxygen and carbon dioxide in critical proportions. By utilizing this special mixture containing oxygen and carbon dioxide in critical proportions, a relatively low and regulated temperature can be obtained. The temperature in the combustion zone within the oil shale structure is preferably kept below about 1000 C. to limit the formation of carbon monoxide. Furthermore, the temperatures in the zones of destructive distillation are controlled to a temperature range above about 400 C. and below about 600 C. Such regulation can be effected by controlling the ratio of carbon dioxide to oxygen in the oxidizing gas fed into the combustion zone. The normal reaction of combustion is:

However, in the presence of an excess amount of carbon dioxide and a temperature in the neighborhood of about 1000 C. the following combustion reaction occurs:

CO2-l-C=2CO-5,850 B. t. u.s

Thus, in the presence of carbon dioxide, two reactions are possible, one exothermic and the other endotherinic. By the use of a predetermined and critical oxygen:carbon dioxide ratio, the temperature can be held relatively uniform across the burning face and the average temperature automatically controlled. The temperature can be further limited and controlled by the diluting effect of the excess carbon dioxide. By such control of oxygenzcarbon dioxide ratio not only can the temperature be controlled, but also the carbon monoxide content of the flue gases from the combustion zone can be kept at a minimum.

The regulation of the temperatures in the zone of destructive distillation has a most desirable effect. It has beend found that as the temperature of the shale rises above 600 C. carbon to hydrogen linkages tend to be progressively broken down and also as the temperature rises, the average molecular Weight of the Volatile products tend to decrease and the evolution of hydrogen, carbon monoxide, methane, etc., increase. It has further been found that in the presence of an excess of carbon dioxide (above 80% in the flue gases) the following desirable effects take place:

(a) The carbon dioxide forms loose temporary compounds with the hydrocarbons as they cool and tend to make these compounds more volatile and thus more quickly and completely removed from the shale.

(b) The carbon dioxide under the conditions brought about in the shale structure will permeate even the smallest of interstices in the structure purging the hydrocarbons that have been adsorbed therein. Such interstices may be native to the structure or deformed by heat or by explosions.

(c) The carbon dioxide under the conditions above described tends to preserve carbon to hydrogen linkages.

(d) Carbon dioxide volumetrically having substantially (almost double) higher specific heat (heat content) than carbon monoxide, nitrogen or other common flue gases, carries more of the heat of combustion to the undecomposed oil shale.

Generally speaking, my improved process for the destructive distillation of oil shale in situ includes the following:

(1) The maintenance of predetermined, controlled temperatures, such as from about 400 C. to about 600 C., in the heating zone of a system for the distillation of hydrocarbons from their underground sources.

(2) The use of a fluid chemical, such as carbon dioxide, having the property of preserving the carbon-hydrogen linkages during the process of distillation.

(3) The use of a fluid which has the properties of being selectively adsorbed in the porous underground structure so as to replace hydrocarbons already adsorbed.

(4) The use of a fluid which has a high heat content to convey heat from combustion zone to zone of distillation.

(5) The use of a fluid which will promote the formation of more volatile hydrocarbon compounds.

(6) The use of a fluid which is of acid nature so as to x and render non-volatile at condenser temperatures, the ammoniacal compounds distilled.

In carrying my invention into practice, it is preferred to control the combustion temperature by the use of a predetermined and critical oxygenzcarbon dioxide ratio in the oxidizing gas. The use of carbon dioxide in the optimum proportion possible to support combustion (say above 20%) in an oxidizing gas mixture is preferred, in order to convey the maximum heat per cubic foot from a combustion zone to a zone in which the heat is required (reaction zone). The use of carbon dioxide as an additive to hydrocarbons at reactive temperatures tends to preserve carbon-hydrogen linkages. The use of carbon dioxide tends to purge out volatile hydrocarbons adsorbed in the interstices of an underground structure, either natural or deformed. The use of carbon dioxide tends to form unstable compounds with the heavier (large molecule) hydrocarbone under pressure, which compounds are found to be more volatile than the heavier hydrocarbons. The use of carbon dioxide in ammoniahydrocarbon mixtures tends to x the ammonia gas as compounds that will separate readily from hydrocarbons in any suitable condensing system.

For the purpose of giving those skilled in the art a better understanding of the invention, the following illustrative example is given:

Oxygen from oxygen tower i is driven by compressor 2 into pipe 3 along with carbon dioxide from Dry Ice liqueer 4. The mixture is regulated by valves 5 and 6 its composition shown on indicator 1 and the temperature of combustion shown by thermometer 8. This oxidizing mixture is driven through pipe 3 to the oil shale structure at the bottom of inlet well 9. In combustion chamber or space I0 (made, for example, by prior use of an explosive) ignition is started by electric spark, thermite or any chemical capable of igniting the oil shale. For a short period of time products and distillation exit through the casing of inlet well 9 and are wasted. As soon as ignition is well started suihcient pressure is built up in the combustion chamber space below well 9, to force products of combustion and distillation through the oil shale structure to outlet well H which may be, say, 50 feet from 'well 9. In passing through the oil shale zone l2 the hot combustion gases distll out of the oil shale the hydroarbons resulting from ,its destruction. There remains in the oil shale a large part of this iixed carbon, in the form of coke. rlhis carbon is burned. by the oxidizing gases in Zone i3 to furnish the hot combustion gases mentioned hereinbefore.

In the system described, the shale sometimes is sufficiently dense that the combustion gases cannot penetrate the outlet Well 5 l. In this case, the structure may be cracked by use of explosives, so as to establish a cracked and permeable zone iiwZ and to permit the passage of these gases from combustion zone i5, to outlet Well l l. The products of destructive distillation of the oil shale accompanied by the products or" combustion and the excess carbon dioxide, flow via the open end or port ll-O and via a plurality of perforations in a perforated zone in? of Well ii and thence upwardly through Well i i to condenser lli. As is Well known, the condenser is provided With a coolant, such as cooling water, which enters coolant inlet itl-I and leaves via coolant outlet lli-O. In addition, condensing Water is introduced into the condenser near the top .plates thereof via water inlet iff-W and leaves the condenser at an intermediate zone thereof, preferably at a plate located just above the middle thereof, via an outlet Ill-WS. In the separate sections or plates of the condenser the heavier hydrocarbons are condensed. and are discharged via hydrocarbon outlet lll-H, the Water soluble compounds are removed by Water via. water soluble outlet iii-WS, and the iixed gases are permitted to escape via vent lll-V, as those skilled in the art will readily understand. In some instances, it may be desirable to place some restriction in the outlet gases from the top I" the condensing tower as a control valve V4 or a control valve Vi in the gas inlet pipe at the bottom of the condenser in order to maintain a back pressure on the burning zone within the oil shale structure. The character oi the distillate is somewhat improved by the distillation under pressure. I have found as a result of tests that combustion under pressure is feasible and readily controlled.

The xed gases be separated from the carbon dioxide in Water under pressure in carbon dioxide separator S or by means of chemicals, the remaining gases, mostly combustible, may be either -further separated or used icr fuel. In come cases Where the combustible gases mixed with the carbon dioxide are in relatively small amounts, this latter separation process may be omitted. rIhe carbon dioxide is returned to a compressor i Where s compressed and is again cycled and mixed with oxygen to form oxidizing gas described hereinbefore.

It is to be observed that the present invention provides an improved process for the destructive distillation or" oil shale in situ involving the fol lowing features:

(l) The use ci' carbon dioxide as a dilutant of oxygen to reduce and control temperatures of combustion.

(2) The use of an oxidizing gas that yields as a flue gas, a high concentration oi carbon dioxide because ci the superior heat carrying capacity per cubic foot of gas of carbon dioxide over the customary flue gases which normally consists of a mixture of gases in which more than 75% is nitrogen. Nitrogen, I und, has volumetrically approximately three-iourths to half o the heat carrying capacity of carbon dioxide.

(3) The mixing of the flue gas with the products of combustion.

(4) The use of carbon dioxide in such a iiue gas to purge out adsorbed hydrocarbons.

(5) The use of carbon dioxide in place of the customary sulfuric acid to fix the ammoniacal compounds in the distillation products.

(6) Carbon dioxide is one of the few commern cial gases which may be readily condensed by increased pressure and reduced temperature so as to separate it from the less condensible gases such as lighter hydrocarbons, nitrogen, monoxide, etc.

Moreover, it is to be appreciated that the present invention provides an improved process for the destructive distillation of oil shale in situ having the following advantageous points:

(l) A control of combustion temperatures by varying the percentage of carbon ydioxide in the oxidizing gases.

(2) The formation of a flue gas that is essentially carbon dioxide and the mixing of such a gas With the products of destructive distillation.

(3) The use of a gas substantially carbon dioxide in underground distillation as the conveyor of heat.

A(4) The use of carbon dioxide to purge out of natural underground structures, hydrocarbons adsorbed therein.

(5) In the destructive distillation of oil shale, coal, etc., the introduction of gases rich in carbon dioxide into the reaction zone to prevent cracking and to promote the preservation of carbon-hydrogen linkages.

(6) The use of carbon dioxide to promote the formation of more volatile hydrocarbon compounds resulting from a destructive distillation.

(7) rihe use of carbon dioxide in ammonia-hydrocarbon mixtures to promote the separation of ammonia and kindred compounds from hydrocarbon mixtures during the process of condensation.

(8) Operations for maintaining a free burning fuel surface by the prevention of the formation of an occluding curtain of slag.

It is to be pointed out that the present invention is concerned solely With the destructive distillation of oil shale in situ and is not to be confused with my co-pending application, Serial No. 64,402 relating to Recovery of Oil From Spent Oil Fields.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art Will readily understand. Such modiiications and variations are considered to be Within the purview and scope of the invention and appended claims.

I claim:

1. .An improved method of destructively distilling oil shale in situ by using a combustion well and an exhaust well extending from the surface of the earth into an oil shale structure and by using a combustion-supporting gas containing carbon dioxide and oxygen in a critical ratio which comprises drawing oxygen from an oxygen tower to provide a supply or oxygen, obtaining carbon dioxide from. a Dry Ice liquefier to provide a supply of carbon dioxide, forming an oxidizing gas mixture with said oxygen and said carbon dioxide, forcing said oxidizing gas mixture under pressure down into a combustion Well extending into an oil shale structure, starting combustion in a combustion Zone adjacent to the base of a combustion well in said oil shale structure, regulating the composition of'said gas mixture to provide a special mixture containing oxygen and carbon dioxide in critical proportion suiiicient to support controlled combustion to give relatively 10W and regulated temperatures thereby preventing the formation of an occluding curtain of slag and facilitating the recovery of hydrocarbons from said oil shale, continuing said combustion with said oxidizing gas mixture and With the production of hot combustion gases, providing at the surface of the earth an indication of the temperature of said combustion in said combustion zone, controlling the temperature of said combustion to below 1000 C. in the combustion zone and a temperature of 400 C. to 600 C. in the zones of destructive distillation by varying the percentage of carbon dioxide to a critical amount above 20% in said oxidizing gas mixture to provide an optimum proportion to support combustion and to convey maximum heat per cubic foot from the combustion zone to said zones of destructive distillation, passing said hot gases from said combustion zone through zones of destructive distillation to a perforated zone in an exhaust Well whereby oil shale is destructively distilled in said structure to produce Volatile hydrocarbons in the presence of a critical amount of carbon dioxide and a minimum amount of carbon monoxide, withdrawing said combustion gases containing said hydrocarbons and said critical amount of carbon dioxide and minimum amount of carbon monoxide through said exhaust well to the surface of the earth, and recovering hydrocarbons from said gases whereby greater yields of volatile hydrocarbons are recovered from said oil shale while at the same time the spent shale is prevented from slagging and the cinder is maintained porous to said gas mixture.

2. An improved method of destructively distilling oil shale in situ by using a combustionsupporting gas containing carbon dioxide and oxygen in a critical ratio which. comprises establishing a combustion Weil extending from the surface of the earth to an. oil shale structure, establishing an exhaust well adiacent to said conibustion well to 'permit withdrawal of hydrocarbons destructively distilled from oil shale in said structure, producing an exploded zone at the bottom of said combustion well and a combustion V zone to facilitate combustion of hydrocarbons in and destructive distillation from said oil shale, ei'lecting combustion in the bottom of said coinbustion well with an oxidizing gas mixture containing carbon dioxide and oxygen, controlling the oxygen-carbon. dioxide ratio in said gas mixture in said combustion well to provide a carbon dioxide content above 20% in said gas mixture and to produce a relatively low and regulated ,emperature below about 1000 C. in the combustion zone and above 400 C. and below about 600 C. in the zones of destructive distillation and to produce an exhaust gas in the exhaust well containing above 80% of carbon dioxide thereby promoting the evolution or" hydrocarbons, withdrawsaid exhaust gas containing volatile hydrocarbons and carbon dioxide from said exhaust well, and recovering said volatile hydrocarbons whereby greater yields of volatile hydrocarbons are recovered from said oil sha-le while at the same time the spent shale is prevented from slagging and the cinder is maintained porous to said gas'mixture, I

3. An improved method of destructively distilling oil shale in situ by using a combustion Well and an exhaust well extending from the surface of the earth into an oil shale structure and by using a combustion-supporting gas containing carbon dioxide and oxygen in a critical ratio which comprises forcing an oxidizing gas mixture consisting mainly of oxygen and carbon dioxide under pressure down into a combustion Well ex tending into an oil shale structure, starting combustion in a combustion zone adjacent to the base of said combustion well in said oil shale str cture, continuing said combustion with said oxidizing gas mixture and with the production of hot combustion gases, providing at the surface of the earth an indication of the temperature of said combustion in said combustion zone, controlling the temperature of said combustion by varying the percentage of carbon dioxide in said oxidizing gas mixture to provide a critical amount of carbon dioxide above 20%, passing hot gases from said combustion zone at controlled and regulated temperatures through said oil shale structure to destructively distill the same to produce volatile hydrocarbons in the presence oi a critical amount of carbon dioxide thereby promoting' evolution of said hydrocarbons, withdrawing said combustion gases containing said hydrocarbons and said critical amount ci carbon dioxide through an exhaust Well to the surface of the earth, and recovering hydrocarbons from said gases whereby greater' yields oi volatile hydrocarbons are recovered from said oil shale while at the same time the spent shale is prevented from slagging and. the cinder is maintained porous to said gas mixture.

4. An improved method of destructively distilling oil shale in situ by using a combustion well and an exhaust well extending from the surface of the earth into an oil shale structure and by using a combustion-suppoitniT gas containing carbon dioxide and oxygen in a critical ratio which comprises burning oil shale in situ in a combustion zone adjacent to the end of a combustion well in the presence of carbon dioxide -to volatilize hydrocarbons from said shale, supporting said burning with oxygen contained in a gas mixture in the presence of a critical amount of carbon dioxide under pressure to produce hot combustion gases, controlling the combustion temperature at a relatively low and regulated tempera-ture by using a critical amount of carlbon dioxide in said gas mixture above 20% in order to support combustion and in order to convey the maximum heat per cubic foot from a combustion zone to zones of destructive distilla tion volatilizing hydrocarbons, maintaining a controlled temperature below 1000c C. in said combustion zone and a controlled temperature within a. range about 400 C. to about 600" C. in the zones of destructive distillation by controlling the ratio of carbon dioxide to oxygen in said gas mixture, withdrawing said combustion gases containing said volatilizecl hydrocarbons and carbon dioxide in a critical amount to the surface of the earth via an exhaust well, and `ecovering hydrocarbons from said gases whereby greater yields of volatile hydrocarbons are recovered from said oil shale while at the same time the spent shale is prevented from slagging and the cinder is maintained porous to said gas mixture.

5. An improved method of destructively iistilling oil shale in situ by using a combustion well and an exhaust well extending from the surface of the earth into an oil shale structure and by using a combustion-supporting gas containing carbon dioxide and oxygen in a critical ratio which comprises forcing an oxidizing gas mixture containing carbon dioxide and oxygen in critical proportions under pressure down into a combustion well located in an oil shale structure, burning oil shale in a combustion zone in the presence of a critical amount of carbon dioxide above 20% at the base of said combustion well with the aid of said oxygen whereby heat is generated at a relatively low and regulated temperature and hot combustion gases are produced containing a critical amount of carbon dioxide, maintaining a critical amount of carbon dioxide in said combustion gases above 80% to :provide relatively low and regulated temperatures, passing said hot combusti-on gases at relatively low and regulated temperatures through an oil shale structure to destructively distill the same to produce vola-tilized hydrocarbons in the presence of a critical amount of carbon dioxide whereby the liberation of said hydrocarbons is facilitated, withdrawing said gases containing said hydrocarbons and carbon dioxide in a critical amount above 80% through an exhaust well to the surface of the earth, and recovering hydrocarbons from said gases whereby greater yields of volatile hydrocarbons are recovered from -said oil shale while at the same time the spent shale is prevented from slagging and the cinder is maintained porous to said gas mixture.

6. An improved method of destructively distilling oil shale in situ by using a combustion well and an exhaust well extending from the surface of the earth into an oil shale structure and by using a combustion-supporting gas containing carbon dioxide and oxygen in a critical ratio which comprises forcing an oxidizing gas mixture containing carbon dioxide and oxygen under pressure into a combustion well located in an oil shale structure; regulating the composition of said gas mixture to provide suincient oxygen to support combustion and to p-rovide an excess of carbon dioxide thereby Icontrolling combustion, maintaining a relatively low temperature, facilitating the evolution of hydrocarbons from said oil shale, preventing cracking f Said volatilized hydrocarbons and promoting the preservation of carbon-hydrogen linkages; burning oil shale in a combustion zone in the presence of a critical amount of carbon dioxide above 20% at the base of said combustion well with the aid of said oxygen whereby heat is generated at a relatively low and regulated temperature and hot combustion gases are produced containing a minimum amount of carbon monoxide; maintaining a critical amount of carbon dioxide in said oxidizing gas mixture and in said combustion gases; passing said combustion gases at relatively low and regulated temperatures through an oil shale structure to destructively distill the same to produce volatilized hydrocarbons in the presence of a critical amount of carbon dioxide and a minimum amount of carbon monoxide whereby the liberation of said hydrocarbons is facilitated, Withdrawing said gases containing said hydrocarbons and carbon dioxide in a critical amount and carbon monoxide in a minimum amount through an exhaust Well to the surface of the earth; and recovering hydrocarbons from said gases whereby greater yields of volatile hydrocarbons are recovered from said oil shale while at the same time the spent shale is prevented from slagging and the cinder is maintained porous to said gas mixture.

7. The improved method set forth in claim 1 in which the gases from the exhaust Well after the recovery of hydrocarbons are treated to separate carbon dioxide for re-cycling to the cornbustion well and re-used therein.

JAMES W. MARTIN.

REFERENCES CITED The following references are of record in the iile of this patent:

UNITED STATES PATENTS Number Name Date 1,269,747 Rogers June 18, 1918 1,342,741 Day June 8, 1920 1,422,204 Hoover et al July 11, 1922 1,473,348 Howard Nov. 6, 1923 1,475,502 Manning Nov. 27, 1923 1,494,735 Cooper May 20, 1924 2,174,336 Walker Sept. 26, 1939 2,174,663 Keller Oct. 3, 1939 2,224,544 Keller Dec. 10, 1940 2,382,471 Frey Aug. 14, 1945 2,390,770 Barton et al. Dec. 11, 1945 FOREIGN PATENTS Number Country Date 193,276 Great Britain Feb. 22, 1923 

2. AN IMPROVED METHOD OF DESTRUCTIVELY DISTILLING OIL SHALE IN SITU BY USING A COMBUSTIONSUPPORTING GAS CONTAINING CARBON DIOXIDE AND OXYGEN IN A CRITICAL RATIO WHICH COMPRISES ESTABLISHING A COMBUSTION WELL EXTENDING FROM THE SURFACE OF THE EARTH TO AN OIL SHALE STRUCTURE, ESTABLISHING AN EXHAUST WELL ADJACENT TO SAID COMBUSTION WELL TO PERMIT WITHDRAWAL OF HYDROCARBONS DESTRUCTIVELY DISTILLED FROM OIL SHALE IN SAID STRUCTURE, PRODUCING AN EXPLODED ZONE AT THE BOTTOM OF SAID COMBUSTION WELL AND A COMBUSTION ZONE OF FACILITATE COMBUSTION OF HYDROCARBONS IN AND DESTRUCTIVE DISTILLATION FROM SAID OIL SHALE, EFFECTING COMBUSTION IN THE BOTTOM OF SAID COMBUSTION WELL WITH AN OXIDIZING GAS MIXTURE CONTAINING CARBON DIOXIDE AND OXYGEN, CONTROLLING THE OXYGEN-CARBON DIOXIDE RATIO IN SAID GAS MIXTURE IN SAID COMBUSTION WELL TO PROVIDE A CARBON DIOXIDE CONTENT ABOVE 20% IN SAID GAS MIXTURE AND TO PRODUCE A RELATIVELY LOW AND REGULATED TEMPERATURE BELOW ABOUT 1000* C. IN THE COMBUSTION ZONE OF DESTRUCTIVE DISTILLATION AND TO C. IN THE ZONES OF DESTRUCTIVE DISTILLATION AND TO PRODUCE AN EXHAUST GAS IN THE EXHAUST WELL CONTAINING ABOVE 80% OF CARBON DIOXIDE THEREBY PROMOTING THE EVOLUTION OF HYDROCARBONS, WITHDRAWING SAID EXHAUST GAS CONTAINING VOLATILE HYDROCARBONS AND CARBON DIOXIDE FROM SAID EXHAUST WELL, AND RECOVERING SAID VOLATILE HYDROCARBONS WHEREBY GREATER YIELDS OF VOLATILE HYDROCARBONS ARE RECOVERED FROM SAID OIL SHALE WHILE AT THE SAME TIME THE SPENT SHALE IS PREVENTED FROM SLAGGING AND THE CINDER IN MAINTAINED POROUS TO SAID GAS MIXTURE. 